In general, known spherical bearings of this type include bearings which are provided with an inside member having a ball portion and an outside member enclosing and holding the ball portion of the inside member to be coupled to the inside member such that the outside member can rock or rotate relative to the inside member. The outside member must undetachably enclose and hold the ball portion against any load acting on the inside member. Therefore, with such a spherical bearing, there remains a problem of what kind of structure to use for sealing the ball portion in the outside member and for securing free rocking and rotational movements of the inside member and the outside member.
In a well-known structural example of the conventionally adopted spherical bearings, the outside member is formed by casting while the ball portion is formed as a core, whereby the ball portion is directly sealed in the outside member (WO 2004/092598). In this spherical bearing, the bearing steel ball serving as the ball portion is covered with the resin liner by injection molding, and the ball portion is set in the die together with the resin liner. After that, the outside member is formed by die-casting of a zinc alloy or an aluminum alloy. The resin liner is heated to adhere to the cast outside member, and they are integrated with each other. Further, the cast outside member clamps the resin liner with respect to the ball portion of the inside member, and hence the rotation of the ball portion with respect to the resin liner becomes heavier. However, when the resin liner is reheated after casting of the outside member, the contact surface pressure of the ball portion and the resin liner is alleviated, with the contact state thereof being maintained. As a result, the ball portion can be held in sliding contact with the resin liner with a significantly small force.
Meanwhile, in another well-known structural example of the spherical bearings, while the ball portion of the inside member is covered with the bearing seat made of a synthetic resin, the outside member is provided with the housing portion to which the bearing sheet is fit, and the ball portion of the inside member is fitted together with the bearing seat with respect to the housing portion (JP 2000-110826 A, JP 2004-278736 A, and JP 2002-161911 A). In the spherical bearing structured as described above, the bearing seat is fitted to the housing portion of the outside member, and then the clamping process is effected with respect to the opening edge of the housing portion. As a result, the bearing seat is prevented from being detached from the outside member, and the ball portion of the inside member is sealed together with the bearing seat in the housing portion of the outside member.
Patent Document 1: WO 2004/092598
Patent Document 2: JP 2000-110826 A
Patent Document 3: JP 2004-278736 A
Patent Document 4: JP 2002-161911 A